Vortex acoustic oscillator

ABSTRACT

Fluid flows tangentially into a curvilinear vortex chamber, creating a central cavitation region; the vortex flow creates a pressure wave at the entrance of a closed-end resonant chamber, which reflects from the closed end of the resonant chamber and propagates substantially radially into the vortex chamber, which increases the fluid static pressure above the vapor pressure of the gas or in the region of cavitation, causing a sudden cessation of cavitation. This, in turn, creates a high pressure wave characterized by acoustical frequencies of a random nature (like white noise), which forces the liquid out of an exit orifice with extremely turbulent flow. When exited into a gaseous environment (such as atmosphere), the stream tends to break up into droplets, each of the droplets having acoustical waves of random yet high frequencies therein; the acoustical waves within the drops tend to assist the formation of droplets as a result of flow sheer. When exited into a liquid, emulsification, outgasing, cleansing and other acoustic functions are enhanced. A second embodiment uses dynamic flow forces to collapse the cavitation region.

United States Patent Goodwin Oct. 14, 1975 [54] VORTEX ACOUSTIC OSCILLATOR [57] ABSTRACT [75] Inventor: R. Wendell Goodwin, Westport, Fluid flows tangentially into a curvilinear vortex Conn. chamber, creating a central cavitation region; the vortex flow creates a pressure wave at the entrance of a [73] Asslgnee' gg i g g Corporatlon closed-end resonant chamber, which reflects from the o closed end of the resonant chamber and propagates [22] Filed: May 31, 1974 substantially radially into the vortex chamber, which increases the fluid static pressure above the vapor [2]] Appl' 475090 pressure of the gas or in the region of cavitation, causing a sudden cessation of cavitation. This, in turn, cre- [52] US. Cl 116/137 A; 15/363; 137/808; ates a high pressure wave characterized by acoustical 239/102 frequencies of a random nature (like white noise), [51] Int. CL F15C 1/16; B06B 3/00; (110K 10/00 which forces the liquid out of an exit orifice with ex- [58] Field of Search 116/137 R, 137 A, 67 R; tremely turbulent flow. When exited into a gaseous 239/101, 102; 137/808, 8l08l3; 15/363 environment (such as atmosphere), the stream tends to break up into droplets, each of the droplets having [56] References Cited acoustical waves of random yet high frequencies UNITED STATES PATENTS therein; the acoustical waves within the drops tend to 2910 s30 11 1959 White 137/810 x assist the formation of droplets as a result of flow 3:]58:166 H964 warren 137/835 sheer. When exited into a liquid, emulsification, out- 3,432,8O4 3/1969 Beeken I I 116/137 gasing, cleansing and other acoustic functions are en- 3,537,465 11/1970 Moore 137/808 x hance A second embodiment uses yn flow 3,620,238 11/1971 Kawabata 137/810 forces to collapse the cavitation region. 3,706,227 12/1972 Gottron 137/808 Primary Examiner-Richard C. Queisser Assistant Examiner-Daniel M. Yasich Attorney, Agent, or FirmM. P. Williams 2 Claims, 3 Drawing Figures US. Patent Oct. 14, 1975 3,911,858

VORTEX ACOUSTIC OSCILLATOR BACKGROUND OF THE INVENTION 1. Field of Invention This invention relates to acoustic oscillators, and more particularly, to a liquid acoustic oscillator employing a vortex chamber and a resonance chamber.

2. Description of the Prior Art There are many industrial applications in which acoustics (pressure waves in a fluid medium) are utilized to promote or enhance physical operations of various sorts. For instance, acoustic waves are induced in cleaning solutions so as to dramatically increase the rate at which machine parts, semiconductors, and other products can be cleansed of various solvents and solutions. The particular phenomena may be a desire to completely and continuously emulsify the solution, or, as in the case of removing ordinary dirt from fibrous cloth, to impart differential mechanical forces, and therefore mutually separating motion, to cloth and particles of foreign substances to be removed therefrom. Emulsification requires breaking down the surface tension of droplets of liquid in another liquid or gas, or bubbles of a gas in a liquid. The process of breaking down the surface tension of liquid drops or bubbles requires the absorption of energy into the liquid droplet or gas bubble, which is most efficient when the pressure wave has a wavelength on the order of twice the size of the particle or the bubble. Maximum mechanical force differential is similarly impressed across a solid particle (such as a particle of dirt) in response to acoustical pressure waves having a wavelength on the order of twice the size of the particle. Therefore, utilization of acoustical waves in applications of this sort are typically best achieved with acoustical waves having frequencies in the tens of kHz. In order to avoid the annoyance which results from audible acoustical waves, such applications frequently utilize ultrasonic waves, the frequency of which is in excess of the useful response frequency of the human ear (in excess of 18 kHz). Thus, the term ultrasonics is most widely used to describe the utilization of acoustical waves in applications of the type described hereinbefore.

Another application in which acoustical energy may be put is the atomization of liquids for a variety of purposes, such as the enhancement of liquid fuel combustion. The principle is the same as in the case of emulsification or outgasing: that is, energy coupled into droplets in the form of an acoustical wave, having a wavelength which is on the order of the size of the droplet or smaller, tends to overcome the surface tension of the droplet, to distort the droplet as a result of variation of pressure force therein, and to aid in breaking the droplet up as a result of these forces and in conjunction with flow sheer forces. However, attempts to couple acoustic energy into liquid drops small enough to be beneficial in combustion processes have failed because the frequencies have been so low as not to create a gradient within the droplets, but rather to cause the droplets to move back and forth in the ambient medium, which in turn, causes them to coalesce into larger drops. This principle is utilized in commercial aerosol agglomerators, and in fact achieves results opposite to that which is desired. Higher frequency energy has been attempted, utilizing a gaseous medium to create the acoustical wave, with an attempt to couple the acoustical energy from the gaseous medium into the liquid.

However, the coupling efficiency of acoustical waves depends upon the relative densities and relative sound velocities in the gaseous medium and the liquid. The coupling efficiency between air and No. 2 fuel oil, for instance, is less than 1/l0th of 1 percent. In fact, it can be shown that devices which operate ostensibly in response to acoustic energy, operate as well with resonant chambers blocked, indicating that the droplet formation is in fact simply the result of sheer forces developed by the flow of the liquid.

Creating acoustical waves in liquid fuels at frequencies high enough to create droplets of a sufficiently small size (on the order of l/ th of an inch or less) requires large numbers of mechanical resonators which are on the order of a fraction of an inch in size. Although large amounts of energy can be mechanically coupled into a liquid, the forces on the energyconverting transducer (such as a resonant plate which is repetitively impacted by a hammer or the like) are so great as to tend to tear the transducer apart. On the other hand, electric transducers, such as piezoelectric or magnetostrictive devices, are limited by virtue of limited temperature tolerance to relatively low energy densities. Such transducers are also extremely expensive, have a tendency toward short life and high maintenance, and require complex and costly driving oscillators which of course, must produce high frequency energy in the same power spectrum or greater than that which is required to induce the acoustical waves desired in the liquid.

SUMMARY OF INVENTION An object of the present invention is to provide improved generation of acoustical waves in a liquid.

According to the present invention, the cavitation region in a vortex formed in a flowing liquid is periodically collapsed by an acoustic wave, generated in a resonant cavity in response to the flow of liquid, so as to generate acoustic waves with high energy content at the cyclic frequency of the resonant cavity. In further accord with the present invention, the acoustic waves drive liquid out of an orifice in pulses at the frequency of the resonator, and additionally induces acoustic waves in the liquid at a variety of frequencies (white noise), which acoustic energy thereby exists internally within droplets formed as a result of the high pressure expulsion of the liquid through an orifice.

In one form of the invention, the exit orifice is more or less in line with the tangential fluid flow inlet to the vortex cavity, and the resonant cavity receives a pressure wave generated by liquid flow from the vortex cavity, thereby interrelating the generation of the resonant acoustic waves with thegeneration of the vortex.

In another form of the invention, the resonant cavity also comprises a curvilinear flow chamber, and the out let orifice may be located centrally of the resonant cavity, leading axially therefrom. In this form of the invention, the dynamic pressure of flow, which has completed the course through the resonant cavity, collapses the cavitation region.

The present invention permits the generation of acoustic waves in a liquid using apparatus having no moving parts. The invention converts energy of the flow of liquid into acoustical energy.

The invention is particularly advantageous in that it provides acoustical energy directly within the liquid itself, instead of simply in a gas medium adjacent the liquid as in the case of many prior art droplet-forming devices. It requires no mechanical, electric or magnetic transducer. Unlike fluidic oscillators and amplifiers which use the Coanda principle, surface effects are not important in an oscillator in accordance with the present invention, so it can be driven as hard as is desired with any liquid flow, and acoustically excited liquid output can be derived therefrom.

The present invention finds utility in atomizing liquids, such as liquid fuels for combustion, as well as in ultrasonic cleaning, degassification, and the like. The present invention can be scaled so as to be equally useful in small or large systems with a variety of flow velocities, energy ranges, and liquid parameters (such as temperature, viscosity, pressure and the like). It is extremely versatile, and the utilization thereof is limited only by its inherent characteristics; substantially all liquid ultrasonic applications can be serviced by apparatus in accordance herewith.

The foregoing and other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of preferred embodiments thereof, as illustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a simplified sectional elevation view of one embodiment of the invention;

FIG. 2 is a simplified sectional elevation view of a modification of the embodiment of FIG. 1; and

FIG. 3 is a simplified sectional elevation view of a second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, a first embodiment of a vortex oscillator in accordance with the present invention comprises a structure 12 having a plurality of cavities therein including an inlet orifice 14 which may be connected to an inlet plenum 16, a curvilinear flow chamber 18 for forming a vortex, a resonance chamber comprising a closed end resonant cavity 20, and an outlet or exit orifice 22. The inlet plenum 16 is adapted for connection to a source of liquid under pressure, such that liquid will flow through the oscillator 10 and out the exit orifice 22, and a portion of the flow is diverted by ajet edge 24 into the vortex chamber 18. The flow in the vortex chamber 18 (as indicated by the solid arrow) forms a cavitation region generally within an area indicated by the dotted line 26. The flow within the vortex chamber 18 impinges on and mixes with the flow between the inlet 14 and the exit orifice 22, and causes a pressure wave to be propagated into the resonant axis of cavity 20. The cavity 20 is basically substantially tangential to the edge of the vortex chamber 18 near the inlet 14, but may be at a slight angle with respect to the tangent in order to be perpendicular with the wavefront which is created by the tangential flow in the vortex chamber 18 in combination with a small normal component resulting from the flow of liquid between the inlet 14 and the exit orifice 22. The precise angle must be determined for any given utilization of the present invention in dependence upon the particular liquid involved, the flow rate, the pressure, viscosity, temperature and the like. This may be determined empirically for maximum pressure output of the device, or it may be calculated at least to a close degree of approximation, utilizing wellknown fluid relationships. The chamber 20 may be perpendicular, as illustrated by the chamber 20a in FIG. 2. There is no flow into the resonant cavity 20, since there is no outlet therefrom; therefore, if desired, the entrance to the resonant cavity 20 could be closed off (as illustrated in FIG. 2) by a resilient diaphragm 28. However, the elastic properties of the diaphragm may tend to cause undesirable damping.

As is known, the flow in a vortex is characterized by extremely low pressure in the center (within the cavitation region 26), and higher pressure for increasing radial distances from the center. Whenever the low pressures in the center is lower than the vaporization pressure of any entrained gases, or of the liquid itself, then small bubbles are formed at the center and tend to propagate outwardly to the edge of the cavitation region 26. The edge of the cavitation region is defined by the pressure at which the bubbles tend to again become entrained within the gas. This is an equilibrium condition with bubbles continuously being formed in the center and disappearing at the edge of the cavitation region.

The bubbles formed in the cavitation region contain a large amount of energy represented in the surface tension of the liquid which surrounds the bubbles. When the bubbles are forced to collapse by a rapid increase in pressure, this energy is given off and creates a pressure wave within the liquid. Thus, as the pressure wave propagates into the resonant cavity 20 and is reflected from the rear wall thereof, this pressure wave exits the resonant cavity and propagates into the vortex chamber 18. When the size of the resonant cavity is chosen with respect to the parameters of the liquid to be resonant at frequencies on the order of lOs of kI-Iz, the pressure gradient is quite steep; this pressure gradient rapidly collapses the gas in the cavitation region, which in turn creates a pressure wave that emanates outwardly in all directions, as from a single distributed source. All of the liquid under the influence of this high pressure wave that results from the collapse of the cavitation region is contained within the liquid itself; some of this energy is in the form of dynamic flow energy in liquid that propagates out through the exit orifice 22 in pulses at the frequency of the resonant cavity 20, and all of the liquid also has within it acoustical waves of a random, relatively high frequency in the nature of white noise as a result of the collapse of the cavitation region 26. As indicated in FIG. 1 by the arrows 30, the liquid may be exited into a gaseous medium; in such a case, the stream of liquid quickly seems to break up into drops, each of which has acoustical waves therein of a random frequency due to the white noise generation resulting from collapse of the cavitation region. The flow of the droplets, however, will be periodic at the frequency of the resonant cavity 20. As the droplets proceed to flow through a gaseous medium, the distortions of the droplets themselves, as a result of the white noise acoustical waves therein, tend to assist in overcoming the surface tension of the droplets by flow sheer among themselves and the gaseous medium, so the droplets break down into still smaller droplets. This results in a very fine atomization of the liquid as it leaves the exit orifice 22. As a result, the invention is particularly well suited to utilization as a liquid atomizer; in fact, the oscillator 10 is extremely well suited as a fuel nozzle for the combustion of liquid fuels, such as in ordinary home oil burners or residual oil burners used for the generation of electricity.

In order to analyze certain of the characteristics of this device in an approximate fashion, consider an oscillator 10 in which the dimension x perpendicular to the paper as shown in FIG. 1 is constant throughout the oscillator 10. Then any area is proportional to any other area by the dimension shown in the sectional view of FIG. 10. Thus, the area, A;, of the inlet orifice 14 may be given as A,-=h x, where h,-=the height of the inlet, i

nd the area of the outlet orifice, A is given as A, h x, where 11,, the height of the outlet. 2

If the vortex chamber is considered to be a circle, and the effective flow area is defined by A of the diameter, d, then the flow area of the vortex, A,., is given as The fluid velocity through the exit, V is given as where C is the discharge coefficient (the ratio of energy per velocity of the inlet of an orifice), compared to the energy per velocity of its outlet.

Ap 'is the pressure difference across the exit orifice 22, and p is the mass density of the liquid.

For water, C can be taken as 0.707 and p is about 10* lb sec so that V0 AP If the average velocity of the flow around the vortex chamber is V then, by continuity of volume of flow,

The time, T, for the liquid to flow from the inlet 14 around the vortex chamber 18 is 1rd 1rd 9 T: V 411,,V, And the frequency, f, of the oscillator 10 is l 411,,V, f= T 6 Substituting equation for V 4h, VA 1.27 11,, VA

5 F... d .05 in.,

10 and Ap= 100 psi,

1270 05 25 kHz, a useful ultrasonic frequency. l2)

Notice in equation 11 that frequency is not dependent upon thickness, x, of the oscillator 10. In other words, the dimension, x, which is perpendicular to the paper as viewed in FIG. 1, may be made as large or as small as desired so as to create the desired magnitude of flow, all of which is acoustically pulsed as described hereinbefore, without altering the frequency of the oscillator 10. Naturally, the principles of the presentinvention may be employed in forms having different shapes than the orthogonal configuration described with respect to FIGS. 1 and 2.

In the embodiment of FIGS. 1 and 2, the inlet 14 need not necessarily be converging, it simply being desired that maximum flow with minimum pressure drop be brought to the inlet 14. Similarly, the exit orifice 22 is not necessarily diverging, nor need it necessarily be flared for maximum impedance match as illustrated in FIG. 1. These are simply good design principles well known in the art which tend to make the device more efficient' and effective. In a similar fashion, design parameters known to those familiar with liquid flow may be utilized, where appropriate, in optimizing the particular design of any vortex acoustical oscillator practicing the principles of the present invention.

A second embodiment of the present invention is illustrated in FIG. 3. Therein, an oscillator 36 employs a curvilinear vortex chamber 18a, which is similar to the vortex chamber 18 of FIG. 1, except that it does not employ a tangential pressure chamber near the inlet 14. The greatest difference, however, is that the oscillator 36 employs dynamic flow forces, rather than static pressure forces, to collapse the cavitation region 26. This is created by a circular flow of fluid in a resonance chamber which consists of a curvilinear chamber 38 which has a centrally disposed, axial outlet 40 therein. The fluid flow from the inlet 14 impinges upon the edge 24a which divides the flow so that circular flow is established in both of the chambers 18a, 38. The flow around the resonant chamber 38, however, is independent of the flow in the vortex chamber 18a, and independently provides the dynamic flow force which impinges upon the cavitation region 26 and collapses it. At the time of collapse, a large pressure wave emanates throughout the device in both chambers 18a, 38 causing a high pressure pulse in the liquid, which in turn creates a pulse of liquid flow out of the orifice 40, the liquid having acoustical waves therein of the nature of white noise as in the embodiment of FIG. 1. This destroys the well ordered, circular flow in each of the chambers 18a, 38, momentarily until the pressure of the created wave subsides below the pressure at the inlet 14, which then reestablishes the two circular flows for the next cycle of operation.

In each of the embodiments, the vortex acoustic oscillator, in accordance with the present invention, operates in accordance with principles of fluid mechanics which are well known. For instance, theories and parameters which are useful in the analysis and design of oscillators in accordance herewith may be found in Binder, R. C., Advanced Fluid Mechanics, (Vols. l and II), 1958: Prentess Hall, Englewood Cliffs, N.J.; and in Hueter, T. F. and Bolt, R. H., Sonics, 1955: John Wiley & Sons, New York, N.Y.. I

As described briefly hereinbefore, the present invention is useful in imparting acoustical energy into liquid, and in creating acoustically controlled flow over liquid. In each of the embodiments, the flow is interrupted by the diversion of the flow at the inlet as a result of either the pressure or the flow of the resonant cavity (20, 38, as the case may be), and as a result of the large pressure wave created upon the collapse of the cavitation region, a large flow is created through the exit orifice (22, 40 as the case may be). Thus, the flow is itself modulated acoustically, and can be controlled to be at a large variety of frequencies from extremely low frequencies to approaching 100 kHz. This amounts to the creation of similar acoustical waves at the resonant frequency if the discharge is into a liquid, such as a container filled with the same liquid that is flowing through the oscillator 10, or in another liquid, with which this liquid is to be mixed or utilized in some other fashion. In addition, however, the liquid itself has acoustical energy stored therein as a result of the collapse of the cavitation region, which acoustical energy is characterized by acoustical waves of random frequencies (similar to white noise). In either case, the acoustical energy is within the liquid itself. Naturally, this energy is dissipated in the form of heat as the result of collisional processes as the liquid flows outwardly from the oscillator 10 in either a gaseous or liquid medium. In the case where the liquid is discharged into a gaseous medium, the pulses of liquid are initially in the form of a stream, but very rapidly atomize into extremely small droplets as a result of flow sheer in combination with the random frequency acoustical energies stored within each droplet of liquid. Thus, the device is useful both to create acoustical waves in liquids and to atomize liquids.

All of the functions which are known to be performable by acoustical waves in liquids can be attained with an oscillator in accordance with the present invention. For instance, the invention may be utilized to create ultrasonic waves in cleaning solutions, to degassify liquids of all sorts, to homogenize liquids, and to vaporize liquids for a variety of purposes. There is an extremely large number of functions and utilizations for which the oscillator of the present invention is well suited, all as is well known in the art.

Although the invention has been shown and described with respect to preferred embodiments thereof,

it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made thereto without departing from the spirit and the scope of the invention. I

Having thus described typical embodiments of my invention, that which I claim as new and desire to secure by Letters Patent of the United States is: i

I. A vortex acoustic oscillator comprising:

a liquid inlet adapted to receive a flow of liquid;

a liquid outlet;

a substantially straight liquid flow path from said inlet to said outlet;

a curvilinear vortex chamber for receiving at least a portion of the flow of liquid from said inlet and for causing the flow of said liquid to be in the form of a vortex characterized by a cavitation region, said vortex chamber being contiguous with and disposed on a first side of said path and having a substantial portion along said path open to said path;

an edge disposed in said flow path between said inlet and said outlet for diverting to said vortex chamber a portion of the liquid flowing from said inlet; and

a closed end resonant chamber disposed substantially perpendicular to said liquid flow path on a side of said path opposite to the'portion of said vortex chamber open to said path, said closed end resonance chamber disposed to respond to liquid flow around said vortex chamber to create pressure waves at a frequency related to the dimensions of said chamber, said pressure waves periodically collapsing said cavitation region thereby causing the liquid to break up into drops and emitting periodic acoustical waves as it exits out.

2. A vortex acoustic oscillator comprising a liquid inlet and a liquid outlet;

a curvilinear vortex chamber having a jet edge for receiving at least a portion of the flow of liquid from said inlet and for causing the flow of said liquid to be in the form of a vortex characterized by a cavitation region; and

a resonance chamber located opposite from said vortex chamber comprising a curvilinear chamber for receiving at least a second portion of the flow of liquid from said inlet and for causing the flow of said liquid therein to be directed toward said cavitation region to collapse it, said resonance chambers having a liquid outlet in the center thereof, said two curvilinear chambers being disposed on opposite sides of said inlet such that the flow from said resonant chamber crosses the flow from said inlet after traversing said resonance chamber thereby causing the liquid to break up into drops and emitting periodic acoustical waves as it exits out. 

1. A vortex acoustic oscillator comprising: a liquid inlet adapted to receive a flow of liquid; a liquid outlet; a substantially straight liquid flow path from said inlet to said outlet; a curvilinear vortex chamber for receiving at least a portion of the flow of liquid from said inlet and for causing the flow of said liquid to be in the form of a vortex characterized by a cavitation region, said vortex chamber being contiguous with and disposed on a first side of said path and having a substantial portion along said path open to said path; an edge disposed in said flow path between said inlet and said outlet for diverting to said vortex chamber a portion of the liquid flowing from said inlet; and a closed end resonant chamber disposed substantially perpendicular to said liquid flow path on a side of said path opposite to the portion of said vortex chamber open to said path, said closed end resonance chamber disposed to respond to liquid flow around said vortex chamber to create pressure waves at a frequency related to the dimensions of said chamber, said pressure waves periodically collapsing said cavitation region thereby causing the liquid to break up into drops and emitting periodic acoustical waves as it exits out.
 2. A vortex acoustic oscillator comprising: a liquid inlet and a liquid outlet; a curvilinear vortex chamber having a jet edge for receiving at least a portion of the flow of liquid from said inlet and for causing the flow of said liquid to be in the form of a vortex characterized by a cavitation region; and a resonance chamber located opposite from said vortex chamber comprising a curvilinear chamber for receiving at least a second portion of the flow of liquid from said inlet and for causing the flow of said liquid therein to be directed toward said cavitation region to collapse it, said resonance chambers having a liquid outlet in the center thereof, said two curvilinear chambers being disposed on opposite sides of said inlet such that the flow from said resonant chamber crosses the flow from said inlet after traversing said resonance chamber thereby causing the liquid to break up into drops and emitting periodic acoustical waves as it exits out. 